Stop trying to speculate and do an actual turn-for-turn battle simulation to determine the winner. For this answer, I'll use these two movesets. Tell me if you think there's a different moveset that's better and I should use.
Charizard @ Choice Specs
EVs: 252 SpA / 4 SpD / 252 Spe
- Blast Burn
Serperior @ Choice Specs
EVs: 252 SpA / 104 SpD / 152 Spe
- Frenzy Plant
These are what their stats come out to be.
(Serperior is faster, so...)
Serperior used Frenzy Plant!
(Frenzy plant is 90% accurate, and deals 291-343 damage, which gives the following outcome a 79% chance of happening.)
Whoever was controlling Serperior won the battle!
So given those two movesets, Serperior will usually win because it's faster.